Phased arrays can be designed to form multiple beams in space and to perform rapid complex or simple scanning of these beams, and provide adaptive capabilities for electronic counter measure purposes.
One of the inviolable laws in the design of electronically scanned phased arrays, defines the relationship between gain-scan volume and the required number of phase controls. This law, referred to as Stangel's Theorem (presented 1974 URSI Spring Meeting Digest), defines "M", the number of phase control elements required and is expressed below in heuristic terms to make a point. ##EQU1## defines M, where M equals the required number of phase shifters.
This relationship states that in order to achieve a given gain over a specified scan volume, "M" phase control elements are required. One can see that an increase in the required gain (read aperture size) and/or the scan volume, necessitates an increase in the number of phase control elements.
While electronically scanned phased arrays have been in use for years at UHF and microwave frequencies, they have been employed in special applications where these arrays were the only viable means of satisfying the antenna requirements. Phase control technology has matured sufficiently at these lower frequencies to permit their use in large arrays.
At millimeter wavelength frequencies, the difficulty of obtaining and using phase control devices is far greater. One known practical means of phase control is ferrite devices. These devices become very expensive at frequencies above 26 GHz and are not amenable to true mass production, causing prices to remain high even in production. In addition, existing ferrite technology provides acceptable performance only to about 60 GHz, and the devices are dimensionally incompatible with the element packing densities required at millimeter wave frequencies. There are other known means (e.g., diode phase shifters) of obtaining control, but these are much too lossy for application at millimeter frequencies unless active apertures are utilized in a manner which provides for establishment of system noise figure independent of the high phase shifter losses. This active aperture technology is being pursued by multiple aerospace firms, currently.
For antenna apertures of appreciable size, the number of required phase shifters can easily be in the thousands. As a result, electronically scanned phased arrays employing ferrite technology become cost prohibitive.
It is known that phase is preserved in the heterodyne process. It has been previously suggested as a scanning technique for single plane scanning.
It is also known that single diodes can be utilized as the radiating elements of a phased array and that they preserve the phase of frequencies which they multiply.
The primary cost driver in the development and production of an electronically scanned phased array has always been the phase control devices (phase shifters) required. For large scan angles and electrically large apertures, the number of phase shifters becomes enormous. This is true because the required element spacing is approximately .lambda..sub.o /2 in both planes and a phase shifter is required behind each element with the required number of phase shifters given by Stangel's theorem as discussed earlier; i.e., number of phase shifters and elements is defined by Gain/Scan volume.
It has long been known that the phase and amplitude information required to steer the beam of a planar array, or an array distributed on a singly curved surface, consists of the superposition of two continuous, orthogonal functions. For an array in the (X,Y) Plane, the required phase functions are .phi.(X) and .phi.(Y). To this point, however, it has been necessary to implement a phase control device at each element in order to achieve the proper superposition for electronic scanning or null steering.
The need exists for electronically scanned phased array systems capable of operating at millimeter wavelength ferquencies and for small, low cost phased array systems.